Cellulosic materials such as paper, wood, and cotton textiles, are highly flammable substances and once ignited continue to burn. Methods for the flame proofing of these materials are known but such methods are either too costly for general commercial use, relatively ineffective, or give rise to products having poor surface character.
With particular reference to paper, methods involving the application of salts of phosphoric acid, boric acid and sulfamic acid are, or have been, used. These methods while commercially attractive, costwise, are troublesome due to the crystallization of such salts on the treated material after drying. Further, the salts crystallize on the application equipment necessitating the frequent shut down of such equipment for cleaning.
Organo phosphorus compounds, such as tetrakis (alpha hydroxyethyl) phosphonium chloride and various derivatives thereof, have also been suggested for the flame proofing of cellulosic materials. Such compounds provide a level of flame retardancy which is at least equivalent to that obtained with the aforementioned phosphate and borate salts. Moreover, the organo phosphorus compounds provide a durable flame retardant character which withstands repeated laundering and dry cleaning. Such compounds, however, because of their relatively high cost, are economically feasible salts only where the durable finish is required.
Accordingly it can be seen that a need exists for a low cost effective method for rendering cellulosic materials fire retardant which methods do not deleteriously affect the surface characteristics of the treated material.